With respect to the ignition of gas flows, for example, in a flare, a distinction may be made between two different ignition techniques. One technique is a point ignition system, where the gas is ignited only at one point. This can be achieved by means of, for example, a match, a pilot burner, or a flame front generator. A prerequisite for point ignition is that the gas, concentration at the point of ignition is between the lower and the upper detonation line. The other technique is a volume ignition system, where ignition occurs through sparks being scattered over a large area and the gas in this area is ignited. The latter technique is a great deal more reliable than the point ignition system.
Norwegian Patent Application No. 932017 teaches a method for the ignition of combustible gas emitted through a flare in a flare tower. The ignition device is a projectile which is fired toward the gas outlet. The ignition device strikes an impact plate mounted at the gas outlet, whereby the ignition device undergoes a reaction and brings a flow of incandescent particles into the gas flow which is ignited. Thus, the ignition device is detonated by impact. This method has a number of inconveniences. For instance, the equipment used is excessively complicated. One reason therefor is that the ignition device is fired by means of very high propulsion gas pressure in the form of a gas pulse, having a pressure of magnitude, 260-300 bar. The manner in which the ignition device is fired makes it impossible to stop the ignition device after it is launched. Also it is not possible to return the ignition device to the launching means. This solution uses a protective tube having a clearance between the ignition pellet (the projectile) and the bore. All the energy for the pellet is supplied before it enters the protective tube (i.e., a normal shot at high pressure).